CAHSEE Math: Mathematical Reasoning Drill 3, Problem 4. Which of the expressions gives the best estimate as to the length of this quadrilateral's perimeter?
|CAHSEE Math||Mathematical Reasoning|
Ok, what is this question asking?
Well yeah, it’s testing our mad rounding skillz…
…but it’s also testing to make sure we can avoid traps.
We should note that our four answer choices apparently went to… 4 very different schools.
“A” rounds up or down to the nearest 10.
B SOMETIMES rounds up, sometimes down, sometimes to the nearest 1, sometimes to the nearest 10...
…and so on. They’re all over the map. In that case, we need to pay attention to
how far away we’re getting from the original number.
A goes down about 4, then down 2, the up almost nothin’, then up 4.
All told, A is only about 2 off the correct total. Not bad.
What about B? Down 4, down almost nothin’, up almost nothin’, and down 6.
Combined, off by 10 or so. No good. C is down 4, down 2, up almost nothin’,
up almost nothin’. Down 6 all day. A is still in the clubhouse with the lead…
Finally, D. Up 6, up almost nothin’, up almost nothin’, down 6.
There are some pretty big swings in there… but at the end of the day, it’s pretty spot on.
Our answer is D.
As in, “Duffer.”